Living
things hold a balance between innovation
and conservation in their gene pools.

As we start to study
reproduction in life
forms, we see two
very important
needs:

The
need to
conserve and
pass down the
information in
the DNA with
no errors

The
need to
provide
variety in the
performance
and
capabilities
of the
organisms

The DNA of all the
living organisms in
a species is called
the gene pool.
Look around
you. The
people that you see
are all recognizably
different from each
other -- but you
have no difficulty
telling a human from
a tree or a dog from
a cat. Each
species has its own
characteristics, and
those
characteristics are
conserved in the
gene pool.
Differences are a
sort of insurance
policy, and can help
some members
of the species
to survive if
the community is
threatened by
disease or
environmental
changes.

Many endangered
animals are
suffering from a
loss of genetic
diversity.
Scientists suggest
that when a species
drops to below 500
animals, it is
likely to be
doomed. One
disease could kill
them all.

We already see
examples of
this.
Cheetahs, for
instance, have
little genetic
diversity due to
some sort of catastrophic
event in the
past. In a
recent incident, a
group of cheetahs in
a zoo picked up a
disease and a third
of them died.
Only two thirds had
whatever genes it
took to survive the
disease.

Dr Viau is more
concerned about
cloning fruit trees
and raising crops
with little genetic
diversity.
During the Irish
Potato Famine in the
1800s all the
potatoes in Ireland
were from the same
stock, and the Irish
farmers depended on
them. When the
potatoes became
diseased and slimy,
a lot of people
starved to
death. Could
something similar
happen in our huge
orchards and immense
grain fields?

Now let's think
about how genetic
changes come about.

We have learned that
organisms inherit
characteristics
which are encoded on
the chromosomes in their
cells. These chromosomes
are passed from parent
to child, and are reshuffled
in each generation through
sexual reproduction.

Some
of the genes that code
for a specific characteristic
come in "different
flavors". For
example, this diagram
shows some genes that
determine eye color.
They are all found on
the same place on the
same chromosome. The
organism will have two
chromosomes, and the
eye color will be determined
by the genes on those
two chromosomes. There
is a variety of eye
colors in this population.

Genes
that are variants of
one another are called
alleles.
They have
the same function, they
are found in the same
location, but what they
determine (eye color
here) is not expressed
identically in all individuals.

Alleles
probably started out
as one gene with one
mode of expression.
Over thousands of
reproductive
copyings, a mistake
was made, and the gene
was changed a little.
Such a change is called
a mutation,
and the individual whose
phenotype (physical
appearance or functioning)
is different is called
a mutant.

Many
mutations cause changes
that are not really
noticeable, but that
may turn out to be useful
someday. For instance,
there appears to be
a mutation that allows
people to become infected
with HIV but not get
sick or die. This mutation
was not valued or noticed,
but perhaps it will
turn out to be really
important. It is rare
in our population, but
could become more common
over the next few centuries.

Some
mutations are lethal.
These cause the organism
which inherits them
to die prematurely.
Some cause death in
infancy or childhood,
so these mutations
are not passed
on. Some cause death
in mid-adulthood or
later, and may
persist
in a population because
they are passed on before
the individual affected
dies.

Nature
is always looking
for the life forms
that are most
successful. If
there were no
mutations, organisms
would reach a high
state of fitness and
then there would be
very little change
in them. This
has worked out well
in extremely stable
environments, such
as the abyssal
plains in the deep
ocean and ancient
tropical rain
forests.
However, if the ice
age comes, or a new
predator is
introduced, or a new
disease appears,
mutations may hold
the very key to the
survival of their
species.

Sometimes
a group of mutations
works together to
allow new
potentialities to
develop. For
instance, it took a
number of mutations
to allow
humans to
become bipedal,
walking on two
legs. As the
species walked more
and more on two
legs, the forepaws
could become hands
and carry
things. This
would favor brain
development as the
creatures figured
out what they wanted
to carry, and
learned to make
tools and
weapons.
Increasing uses for
the hands would
benefit from better
thinking in the
brain. Useful
mutations are
retained, and life
forms change in
response to changes
in themselves and
the environment.